Dual duty compression machine

ABSTRACT

A compression machine includes a refrigerant condenser, an expansion device, a refrigerant evaporator, a first compressor and a second compressor. Each compressor is arranged to receive lower pressure refrigerant vapor from the evaporator and to deliver higher pressure vapor to the condenser independently of the other compressor. The first compressor operates when the compression machine is operating in a first duty mode, for example a water-cooling mode. The second compressor operates when the compression machine is operating in a second duty mode, for example one of a water-heating mode or a brine cooling. The first compressor is selected for optimal performance in the first duty only and the second compressor is selected for optimal performance in the second duty mode only.

CROSS-REFERENCE TO RELATED APPLICATION

Reference is made to and this application claims priority from and the benefit of U.S. Provisional Application Ser. No. 61/167,978, filed Apr. 9, 2009, entitled “DUAL DUTY COMPRESSION MACHINE”, which application is incorporated herein in its entirety by reference.

FIELD OF THE INVENTION

This invention relates generally to compression machines for building cooling and heating application or ice thermal storage application and, more particularly, to a compression machine having dual compressors, one compressor dedicated for water chilling and the other compressor dedicated for water heating or ice thermal storage.

BACKGROUND OF THE INVENTION

Compression machines are well known for use in providing chilled water for use in air conditioning systems for buildings, especially large commercial buildings. A common type of compression chiller includes a tube-in-shell heat exchanger that functions as a refrigerant vapor condenser, a tube-in-shell heat exchanger that functions as a refrigerant liquid evaporator, and a centrifugal compressor that has an inlet in refrigerant flow communication with the evaporator and an outlet in refrigerant flow communication with the condenser. In the condenser, water is passed through the heat exchange tubes in heat exchange relationship with hot refrigerant vapor discharged from the compressor into the shell of the condenser and flowing over the heat exchange tubes. In doing so, the refrigerant vapor is condensed and the water flowing through the heat exchange tubes is heated. The condensed liquid refrigerant is passed through an expansion device and thereby expanded to form a lower pressure, lower temperature refrigerant liquid/vapor mixture. The refrigerant liquid/vapor mixture is delivered into the shell of the evaporator and dispersed to flow over the heat exchange tubes therein. In the evaporator, water passing through the heat exchange tubes is cooled and the refrigerant liquid/vapor mixture is heated and the liquid refrigerant evaporated. The refrigerant vapor exits the shell of the evaporator and passes back the inlet of the compressor, thereby completing the refrigerant flow circuit.

Compression machines of this type may also be used for heating water in the winter for building space heating purposes, in addition to cooling water in the summer for building air conditioning purposes. However, designing the compression machine for dual purposes, i.e. both water-cooling in the summer and water heating in winter is complicated due to the quite different temperatures of the water supplied to the compression machine and differing temperature required to be supplied to the building for cooling/heating. The lift required for water heating in the winter may be nearly twice the lift required for water-cooling in the summer. Consequently, in compression machines designed with a single compressor, the compressor must be selected to provide sufficient capacity to meet the winter heating lift requirement, and then be operated at a substantially reduced capacity during the summer cooling season to match the reduced summer cooling lift requirement. Unfortunately, compressors operating at a substantially reduced capacity, in particular centrifugal compressors operating at a substantially reduced capacity, suffer a significant reduction in energy efficiency, leading to a waste of energy and increased power consumption costs.

Although compression machines of this type typically employ a single compressor, compression machines employing two compressors are also known. For example, a compression chiller using two individual centrifugal compressors arranged in series is disclosed in U.S. Pat. No. 5,875,637. As disclosed therein, the first compressor receives through its inlet low pressure refrigerant vapor from the evaporator and discharges refrigerant vapor at an intermediate pressure to the inlet of the second compressor. The refrigerant vapor is further compressed in the second compressor and discharged to the condenser at a relatively higher discharge pressure.

Another example of a compression machine having two centrifugal compressors is disclosed in U.S. Pat. No. 3,859,820. As disclosed therein, the compression machine includes an evaporator, a condenser divided into two separate chambers, and two separate centrifugal compressors are in parallel. Each compressor receives as its input refrigerant vapor from the evaporator. However, each compressor discharges compressed refrigerant vapor into a respective separate one of the chambers of the condenser.

In such two-compressor compression machines, increased capacity may be achieved relative to single compressor compression machines as both compressors, whether disposed in a series arrangement or a parallel arrangement, are operated simultaneously. In the series arrangement of the two centrifugal compressors, the increased capacity is attainable because the individual rises in refrigerant pressure developed in the separate compressors is additive. In the parallel arrangement of the two centrifugal compressors, the increased capacity is attainable because the overall refrigerant throughput is the sum of the refrigerant flows through the two centrifugal compressors. However, the increased capacity comes at a price, as each compressor must have its own drive motor, starter and controls. Additionally, the overall system controls are necessarily more complicated.

SUMMARY OF THE INVENTION

In an aspect of the invention, a compression machine provided for selective operation in one of a first duty mode and a second duty mode. The compression machine includes: a refrigerant condenser, an expansion device, a refrigerant evaporator, and a compression device disposed in a serial refrigerant flow relationship. The compression device includes a first compressor and a second compressor, each of which is arranged to receive lower pressure refrigerant vapor from the evaporator and to deliver higher pressure vapor to the condenser independently of the other. The first compressor is selected for optimum operation of the compression machine in the first duty mode and the second compressor is selected for optimum operation of the compression machine in the second duty mode. In an embodiment, the first duty mode has a first lift requirement and the second duty mode has a second lift requirement that is greater than the first lift requirement. In an embodiment, the first duty mode may be a water-cooling mode and the second duty mode may be one of a water-heating mode or a brine cooling mode.

A controller may be provided in operative association with each of the first compressor and the second compressor, selectively operates the first compressor when operating the compression machine in a water-cooling mode and selectively operates the second compressor when operating the compression machine in a water-heating mode. The controller directs electric power to a first drive motor for driving the first compressor when operating the compression machine in a water-cooling mode and directs electric power to a second drive motor for driving the second compressor when operating the compression machine in a water-heating mode. In an embodiment, each of the first compressor and the second compressor comprises a centrifugal compressor.

In an aspect of the invention, a method is provided for operating a compression machine for selectively cooling water or heating water, the compression machine having a condenser and an evaporator in refrigerant flow communication with the condenser, a first compressor for receiving refrigerant vapor from the evaporator and delivering refrigerant vapor to the condenser, and a second compressor for receiving refrigerant vapor from the evaporator and delivering refrigerant vapor to the condenser. The method includes the steps of: selectively operating the compression machine in one of a water cooling mode or a water heating mode; operating the first compressor when operating the compression machine in a water cooling mode; and operating the second compressor when operating the compression machine in a water heating mode.

In an aspect of the invention, a method is provided for designing a compression machine for selective operation in one of a first duty mode or a second duty mode, the compression machine having a condenser and an evaporator in refrigerant flow communication with the condenser, a first compressor for receiving refrigerant vapor from the evaporator and delivering refrigerant vapor to the condenser, and a second compressor for receiving refrigerant vapor from the evaporator and delivering refrigerant vapor to the condenser. The method includes the steps of: selecting the first compressor to perform optimally in the first duty mode, and selecting the second compressor to perform optimally in the second duty mode. In an embodiment, the first duty mode has a first lift requirement and the second duty mode has a second lift requirement that is greater than the first lift requirement. In an embodiment of the method, the step of selecting the first compressor to perform optimally in the first duty mode comprises selecting the first compressor to perform optimally in a water-cooling mode; and the step of selecting the second compressor to perform optimally in the second duty mode comprises selecting the second compressor to perform optimally in one of a water-heating mode or a brine-cooling mode.

BRIEF DESCRIPTION OF THE DRAWINGS

For a further understanding of the disclosure, reference will be made to the following detailed description which is to be read in connection with the accompanying drawings, where:

FIG. 1 is perspective view of an exemplary embodiment of a compression machine in accordance with the invention;

FIG. 2 is a schematic diagram depicting the compression machine of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawing, there is depicted therein an exemplary embodiment of a compression machine, designated generally by the reference numeral 10. The compression machine 10 includes a refrigerant condenser 20, an expansion device 25, a refrigerant evaporator 30, and a compression device disposed in a serial refrigerant flow relationship. The compression device includes a first compressor 40 and a second compressor 50, each of which is arranged to receive lower pressure refrigerant vapor from the evaporator 30 and to deliver higher pressure refrigerant vapor to the condenser 20 independently of the other. Separate drive motors 42, 52 are provided in operative association with the first compressor 40 and the second compressor 50, respectively. The first drive motor 42 drives only the first compressor 40. The second drive motor 52 drives only the second compressor 50. In the depicted exemplary embodiment, each of the first compressor 40 and the second compressor 50 comprises a centrifugal compressor.

The condenser 20 is a liquid-cooled condenser and may any one of various conventional designs. For example, for purposes of illustration, but not limitation, the condenser 20 may be a tube-in-shell condenser, wherein a heat transfer fluid, most commonly, and in the application described herein, water, is passed through a multiple-tube heat exchanger (not shown) housed in a closed shell into which is introduced high pressure, high temperature refrigerant vapor discharged from the compression device. The high temperature refrigerant passes over the exterior of the tubes of the heat exchanger in heat exchange relationship with the water passing through the tubes of the heat exchanger, whereby the refrigerant vapor is cooled and condensed to a refrigerant liquid and the water is heated.

The high pressure, condensed refrigerant liquid passes from the condenser 20 to the evaporator 30 through a refrigerant passage 11 in which is disposed an expansion device 25. As the high pressure refrigerant liquid traverses the expansion device 25, the refrigerant liquid expands to a lower pressure and a lower temperature to form a refrigerant vapor or a saturated mixture of refrigerant liquid and refrigerant vapor at the lower pressure and the lower temperature. The lower pressure, lower temperature vapor or liquid/vapor mixture is delivered via the passage 11 to and introduced into the shell of the evaporator 30.

The evaporator 30 also may any one of various conventional designs. For example, for purposes of illustration, but not limitation, the evaporator 30 may be a tube-in-shell evaporator, wherein a heat transfer fluid, most commonly, and in the application described herein, water or a chemical salt solution (brine), is passed through a multiple-tube heat exchanger (not shown) housed in a closed shell into which is introduced the lower pressure, lower temperature refrigerant liquid in traversing the expansion device 25. The lower temperature refrigerant liquid collects in the shell immersing the tubes of the heat exchanger. Thus, the water or brine passing through the tubes passes in heat exchange relationship with the liquid refrigerant in which the tubes are immersed, whereby the refrigerant liquid is heated and evaporated to a refrigerant vapor and the water or brine is cooled.

As noted previously, the first compressor 40 and the second compressor 50 are each arranged in the refrigerant flow circuit between the evaporator 30 and the condenser 20. A refrigerant line 47 has an outlet opening into the shell of the condenser 20 and an inlet in communication with the discharge outlet of the first compressor 40 whereby the first compressor 40 discharges higher pressure, hot refrigerant vapor into the condenser 20. Similarly, a refrigerant line 57 has an outlet opening into the shell of the condenser 20 and an inlet in communication with the discharge outlet of the second compressor 50 whereby the second compressor 50 discharges higher pressure, hot refrigerant vapor into the condenser 30.

A refrigerant line 43 has an inlet opening into the shell of the evaporator 30 and an outlet in communication with the suction inlet of the first compressor 40 whereby the first compressor 40 receives lower pressure refrigerant vapor from the evaporator 30. Similarly, a refrigerant line 53 has an inlet opening into the shell of the evaporator 30 and an outlet in communication with the suction inlet of the second compressor 50 whereby the first compressor 50 receives lower pressure refrigerant vapor from the evaporator 30. A first flow shut-off valve 45 is interdisposed in refrigerant line 43 upstream with respect to refrigerant flow of the suction inlet to the first compressor 40. A second flow shut-off valve 55 is interdisposed in refrigerant line 53 upstream with respect to refrigerant flow of the suction inlet to the second compressor 50.

The compression machine 10 may also include a control system 80 for selectively operating the first compressor 40 and the second compressor 50. The control system may include a first controller 80-1 that is operatively associated with the first compressor 40 and its drive motor 42 and a second controller 80-2 that is operatively associated with the second compressor 50 and its drive motor 52, and a motor starter 82 that is capable of selectively starting either the first compressor 40 or the second compressor 50 as directed. The control system may also include a master controller (not shown) that selectively independently commands the first and second controllers 80-1, 80-2. In other embodiments, the control system 80 associated with the compression machine 10 may include a single controller for controlling the first and second compressors 40, 50 respectively. In the illustrated embodiment, the control system 80 may be configured to operate the compression machine 10 in a water-cooling mode during the summer cooling season to supply chilled water to an air conditioning system (not shown) of a building associated with the compression machine 10. The control system 80 operates the compression machine 10 in a water-heating mode during the winter heating season to provide hot water to the air conditioning system of a building associated with the compression machine 10. For example, for purposes of illustration, but not limitation, the compression machine 10 may need to supply chilled water at a temperature in the vicinity of about 7° C. (about 45° F.) during the summer cooling system, and need to supply hot water at a temperature in the vicinity of about 50° C. (about 122° F.) during the winter heating season. Thus, the lift requirement associated with water-cooling duty would be less than the lift requirement associated with water-heating duty.

In another application, the control system 80 may be configured during the summer to operate the compression machine 10 in a brine-cooling mode to supply chilled brine to an air conditioning system (not shown) of a building associated with the compression machine 10 during the hours of the day when the building is occupied and to supply chilled brine to an ice-storage system (not shown) to make ice during the hours of the night when the building occupancy is lower, such as typically at night. Chilling brine for the air-conditioning duty would have a lower lift requirement than chilling brine for ice-making duty.

The compression machine 10 is designed for selective operation in one of a first duty mode and a second duty mode. The first compressor 40 is selected for optimal operation of the compression machine 10 in the first duty mode, for example a water-cooling mode, and the second compressor 50 is selected for optimal operation of the compression machine 10 in the second duty mode, for example a water-heating mode or a brine cooling mode. In an embodiment, first compressor 40 is selected for optimal operation of the compression machine for providing chilled water passing from the refrigerant evaporator at a temperature in the range of from about 2° C. to about 12° C. (about 35° F. to about 54° F.). In an embodiment, second compressor 50 is selected for optimal operation of the compression machine for providing heated water passing from the refrigerant condenser at a temperature in the range of from about 40° C. to about 60° C. (about 104° F. to about 140° F.). In an embodiment, the second compressor 50 is selected for optimal operation of the compression machine 10 for providing chilled brine to an ice thermal storage system (not shown) for use in making ice.

To operate the compression machine 10 in the first duty mode, for example the water-cooling mode, the controller 80 closes the flow shut-off valve 55 in refrigerant line 53 thereby isolating the second compressor 50 from the refrigerant circuit, supplies electric power to the starter 82, and commands the starter 82 to activate the first drive motor 42 for driving only the first compressor 40. Alternately, to operate the compression machine 10 in the second duty mode, for example the water-heating mode or brine cooling mode, the controller 80 closes the flow shut-off valve 45 in refrigerant line 43 thereby isolating the first compressor 40 from the refrigerant circuit, supplies electric power to the starter 82, and commands the starter 82 to activate the second drive motor 52 for driving only the second compressor 50. Therefore, when operating the compression machine 10 in the first duty mode, the first compressor 40 is operated and the second compressor 50 is shutdown and isolated from the refrigerant circuit. Conversely, when operating he compression machine 10 in the second duty mode, the second compression 50 is operated and the first compressor 40 is shut down and isolated from the refrigerant circuit.

The compression machine 10 is designed for optimal energy efficiency in both the water-cooling mode and the water-heating or brine cooling mode by selecting as the first compressor 40 a first compressor selected to perform optimally in a water cooling mode only, and by selecting as the second compressor 50 a second compressor selected to perform optimally in one of a water heating mode or brine cooling mode. By selecting the second compressor 50 for optimal capacity and efficiency in the water heating mode or ice storage mode, wherein the lift required could be as much as about twice the lift required in the water cooling mode, the first compressor 40 may be selected for optimal efficiency and performance to meet the lower lift demands, while the second compressor 50 may be selected for optimal efficiency and performance to meet the higher lift demands. For example, in the winter, water for delivery to the evaporator 30 may be drawn from a outside water source at a temperature of about 7° C. (about 45° F.) and the hot water leaving the condenser 20 to meet space heating demand may need to be at a temperature of about 50° C. (about 122° F.), while in the summer, water for delivery to the condenser 20 may be from the outdoor water source at a temperature of about 32° C. (about 90° F.) and the chilled water leaving the evaporator 30 to meet air conditioning demand may need to be at a temperature of about 7° C. (about 45° F.). With a typical single compressor compression machine, the designer would necessarily need to size the compressor to meet the maximum lift requirement and compression capacity demand associated with the second duty mode and simply expect lower than optimal efficiency performance during operation in the first duty mode. However, the compression machine 10 of the invention provides for optimal performance in both the lower lift requirement first duty mode and the higher lift requirement second duty mode.

Additionally, in an embodiment the first compressor 40 and the second compressor 50 are designed to not operate at the same time. In this embodiment, the first compressor 40 is selected for operation in, and is only operated, when the compression machine 10 operates in the water-cooling mode, and the second compressor 50 is selected for operation in, and is only operated, when the compression machine 10 operates in the water-heating mode. In this embodiment, only one motor starter 82.

Referring now to FIG. 1, it should be noted that the second compressor 50, which is the compressor selected for operation in the second duty mode, that is the duty mode having the higher lift requirement, is positioned opposite the end at which the water enters the evaporator. In practice, the second compressor 50 should be positioned as far as practical from the water inlet end to the condenser to avoid liquid carry-over inside the evaporator, which is driven by the pressure difference between the condenser and the evaporator.

The terminology used herein is for the purpose of description, not limitation. Specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as basis for teaching one skilled in the art to employ the present invention. While the present invention has been particularly shown and described with reference to the exemplary embodiments as illustrated in the drawing, it will be recognized by those skilled in the art that various modifications may be made without departing from the spirit and scope of the invention. Those skilled in the art will also recognize the equivalents that may be substituted for elements described with reference to the exemplary embodiments disclosed herein without departing from the scope of the present invention.

Therefore, it is intended that the present disclosure not be limited to the particular embodiment(s) disclosed as, but that the disclosure will include all embodiments falling within the scope of the appended claims. 

1. A dual duty compression machine for selective operation in one of a first duty mode and a second duty mode comprising: a refrigerant condenser, an expansion device, a refrigerant evaporator, and a compression device disposed in a serial refrigerant flow relationship, said compression device including a first compressor and a second compressor, each of said first compressor and said second compressor arranged to receive lower pressure refrigerant vapor from said evaporator and to deliver higher pressure vapor to said condenser independently of the other of said first compressor and said second compressor, said first compressor selected for optimal operation of said compression machine in the first duty mode and said second compressor selected for optimal operation of said compression machine in the second duty mode.
 2. The compression machine as recited in claim 1 further comprising a control system operatively associated with each of said first compressor and said second compressor for selectively operating said first compressor when operating said compression machine in the first duty mode and for selectively operating said second compressor when operating said compression machine in the second duty mode.
 3. The compression machine as recited in claim 1 wherein at least one of said first compressor and said second compressor comprises a centrifugal compressor.
 4. The compression machine as recited in claim 1 further comprising a first drive motor operatively associated with said first compressor only and a second drive motor operatively associated with said second compressor only.
 5. The compression machine as recited in claim 4 wherein said control system is configured to direct electric power to said first drive motor when operating said compression machine in the first duty mode and direct electric power to said second drive motor when operating said compression machine in the second duty mode.
 6. The compression machine as recited in claim 1 wherein the first duty mode has a first lift requirement and the second duty mode has a second lift requirement, the second lift requirement being greater than the first lift requirement.
 7. The compression machine as recited in claim 1 wherein the first duty mode is a water-cooling mode and the second duty mode is a water-heating mode.
 8. The compression machine as recited in claim 1 wherein the first duty mode is a water-cooling mode and the second duty mode is a brine-cooling mode.
 9. The compression machine as recited in claim 1 wherein the first duty mode is a water-cooling mode and the second duty mode is one of a water-heating mode and an ice-making brine-cooling mode.
 10. A method for designing a compression machine for selective operation in one of a first duty mode or a second duty mode, the compression machine having a condenser and an evaporator in refrigerant flow communication with the condenser, a first compressor for receiving refrigerant vapor from the evaporator and delivering refrigerant vapor to the condenser, and a second compressor for receiving refrigerant vapor from the evaporator and delivering refrigerant vapor to the condenser, said method comprising the steps of: selecting the first compressor to perform optimally in the first duty mode; and selecting the second compressor to perform optimally in the second duty mode.
 11. The method for designing a compression machine as recited in claim 10 wherein: the step of selecting the first compressor comprises selecting a first centrifugal compressor to perform optimally in the first duty mode only; and the step of selecting the second compressor comprises selecting a second compressor to perform optimally in the second duty mode only.
 12. The method as recited in claim 11 wherein the first duty mode has a first lift requirement and the second duty mode has a second lift requirement, the second lift requirement being greater than the first lift requirement.
 13. The method as recited in claim 10 wherein the step of selecting the first compressor to perform optimally in the first duty mode comprises selecting the first compressor to perform optimally in a water-cooling mode; and the step of selecting the second compressor to perform optimally in the second duty mode comprises selecting the second compressor to perform optimally in one of a water-heating mode or a brine-cooling mode.
 14. A method for operating a compression machine for selectively cooling water or heating water, the compression machine having a condenser and an evaporator in refrigerant flow communication with the condenser, a first compressor for receiving refrigerant vapor from the evaporator and delivering refrigerant vapor to the condenser, and a second compressor for receiving refrigerant vapor from the evaporator and delivering refrigerant vapor to the condenser, said method comprising the steps of: selectively operating the compression machine in one of a water cooling mode or a water heating mode; operating the first compressor only when operating the compression machine in a water cooling mode; and operating the second compressor only when operating the compression machine in a water heating mode.
 15. The method for operating a compression machine as recited in claim 14 wherein the first compressor is selected to perform optimally in a water chilling mode and the second compressor is selected to perform optimally in a water heating mode.
 16. The method for operating a compression machine as recited in claim 15 wherein at least one of the first compressor and the second compressor comprises a centrifugal compressor.
 17. The compression machine as recited in claim 1 wherein said first compressor is selected for operation of the compression machine for providing chilled water passing from the refrigerant evaporator at a temperature in the range of from about 2° C. to about 12° C. (about 35° F. to about 54° F.).
 18. The compression machine as recited in claim 1 wherein said second compressor is selected for operation of the compression machine for providing heated water passing from the refrigerant condenser at a temperature in the range of from about 40° C. to about 60° C. (about 104° F. to about 140° F.). 